This invention relates to a polyethersulfone composition, a method to synthesize the polyethersulfone composition and articles made from the compositions.
Polyethersulfones are typically linear, amorphous, injection moldable polymers possessing a number of desirable features such as excellent high temperature resistance, good electrical properties and toughness. Due to their excellent properties, the polyethersulfones can be used to manufacture a variety of useful articles such as molded articles, films, sheets and fibers. The polyethersulfones offer high chemical and solvent resistance and are particularly useful for manufacturing articles that are exposed to solvents or chemical agents at elevated temperatures and for extended times. Thus, they find application in articles such as medical trays, which are subjected to repeated and rigorous sterilization procedures.
Many of the articles made from polyethersulfones are manufactured by injection or other molding processes. Although the currently available polyethersulfones have been very successful for the manufacture of molded articles, there is a continuing need for polyethersulfones of improved combinations of properties such as improved melt flow characteristics so that molding operations can be performed more rapidly and with improved economics. Also it is desirable that the polyethersulfone composition has good impact and heat resistance without the consequent loss of other desirable characteristics. Typically, it is difficult to obtain good flow, high impact strength and high heat resistance in a particular polyethersulfone composition.
British patent GB 1,264,900 teaches a process for production of a polyethersulfone comprising structural units derived from equimolar amounts of the reactants 4,4′-biphenol and bisphenol-A (4,4′-isopropylidenediphenol). However, the patent requires that the said reactants be present in amounts deviating from equimolar by no more than plus/minus 5 mole %.
U.S. Pat. No. 6,228,970 describes polyethersulfones comprising structural units derived from 4,4′-biphenol. However, this patent does not teach or suggest any relationship between the content of structural units derived from biphenol and the minimum molecular weight of the polyethersulfone necessary to obtain an optimum balance of physical properties. Therefore, there is a continuing need for polyethersulfones possessing a balanced property profile including high impact strength and good flow properties.
U.S. Pat. No. 4,814,419 describes polyethersulfones comprising structural units derived from bisphenol A and 4,4′-biphenol. However, this patent does not teach or suggest any relationship between the content of structural units derived from 4,4′-biphenol and bisphenol A, and the minimum molecular weight of the polyethersulfone necessary to obtain high strength materials displaying Notched Izod values superior to commercially available polyethersulfones such as RADEL R, a commercially available polyethersulfone comprising structural units derived from 4,4′-biphenol and a bis(4-halophenyl)sulfone. U.S. Pat. No. 4,814,419 discloses a polyethersulfone composition comprised of structural units derived from a bis(4-halophenyl)sulfone, 4,4′-biphenol and bisphenol A, the structural units derived from 4,4′-biphenol and bisphenol A being present in a molar ratio of 75:25. While the reference does not report a molecular weight, a glass transition temperature is provided for the 75:25 material. The reported glass transition temperature, 205° C., corresponds to a weight average molecular weight (Mw) of less than 54,000 grams per mole as determined by gel permeation chromatography.